A deficit of normal tissue in a subject may result from, for example, burns, tumor resection surgery (e.g., mastectomy), or congenital deformities. Often, the tissue in deficit is skin and/or underlying connective tissue. The tissue in deficit can also be an intrabody duct (e.g., urethras or GI tract).
One method of correcting skin deficit is to stimulate creation of new skin. Implantation of a device that expands and stretches the existing skin causes a growth response in which new skin is created.
The first report of tissue expansion was in 1956 by Charles Neumann (Plastic & Reconstructive Surgery; Vol 19 (2); 124-130) who implanted a rubber balloon attached to a percutaneous tube to enable intermittent expansion for the purpose of reconstructing a partially amputated ear. Since that time, the idea of tissue expansion devices has undergone commercial development.
Most commercially available tissue expanders function as an implantable balloon with an extracorporeal or imbedded valve that allows periodic inflation. Typically, it is a doctor that performs the inflation. Since the inflation events are relatively infrequent, a significant inflation pressure is typically applied at each doctor's visit in order to achieve maximum effect from each visit. As a result of this inflation pressure during a clinic visit, a relatively sudden tissue stretch occurs. This may cause subjects to suffer discomfort and/or tissue ischemia. The relatively large inflation pressure can also adversely affect underlying structures (e.g., cause concavities in underlying bone). In addition, high pressure may create restrictive capsules around the implant and/or cause tissue failure. Some previously available alternatives used a needle for inflation or filling, creating a potential source of infection.
In order to overcome such issues, continuously expanding devices have been developed. For example, osmotic expanders have been reported by Austad in 1979, Berge in 1999, and Olbrisch in 2003 (see U.S. Pat. Nos. 5,005,591 and 5,496,368). A commercial version is available from Osmed Corp. in a limited range of sizes. These devices use a polymeric osmotic driver to expand a silicone implant by absorbing interstitial fluid (ISF). A potential problem of such devices is the lack of control or adjustability after implantation with respect to expansion variables such as pressure, volume, onset of expansion, and end of expansion once they have been deployed.
U.S. Pat. No. 6,668,836 to Greenberg et al. describes a method for pulsatile expansion of tissue using an external hydraulic pump. The external hydraulic pump is bulky and may lead to negative subject reactions. The percutaneous attachment reduces subject mobility and may be a source of contamination. U.S. Pat. No. 4,955,905 to Reed teaches an external monitor for pressure of an implanted fluid filled tissue expansion device. U.S. Pat. Nos. 5,092,348 and 5,525,275 to Dubrul and Iverson respectively teach implantable devices with textured surfaces. U.S. Patent Publication No. 2004/0147953 by Gebedou teaches a device which relies upon an internal mechanical force as a means of avoiding use of fluids for tissue expansion. U.S. Pat. Nos. 6,264,936; 6,180,584; 6,126,931; 6,030,632; 5,869,073; 5,849,311 and 5,817,325 deal generally with the concept of antimicrobial coatings.
The disclosure herein describes tissue expanders and methods of use that overcome shortcomings of existing tissue expanders.